1. Magnetic float level gauge

A.working principle.

Developed based on the principle of buoyancy and magnetic coupling. When the liquid level in the tested container rises or falls, the magnetic float in the liquid level gauge body tube also rises or falls accordingly. The magnetic steel inside the float is transmitted to the magnetic flip column indicator through magnetic coupling, driving the red and white flip columns to flip. When the liquid level rises, the flip column changes from white to red, and when the liquid level drops, it changes from red to white. The red white boundary of the indicator is the actual height of the liquid level inside the container, thus achieving clear indication of the liquid level.

B.advantage.

It can achieve high sealing, leak prevention, and is suitable for high temperature, high pressure, and corrosion-resistant applications. It is more effective against high temperature, high pressure, toxic, harmful, and highly corrosive media.

C.shortcoming.

When in direct contact with the medium, the sealing requirements for the floating ball must be strict and cannot measure viscous media. Magnetic materials such as demagnetization can easily cause the liquid level gauge to malfunction

2. Electromagnetic wave radar level gauge(Guided wave radar level gauge)

Aworking principle.

Radar level gauge adopts transmissionThe working mode of reflection reception. The antenna of the radar level gauge emits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time from emission to reception of electromagnetic waves is proportional to the distance to the liquid surface, and the relationship is as follows:

D=CT/2

(D: Distance from radar level gauge to liquid level C: Speed of light T: Electromagnetic wave travel time)

The radar level gauge records the time elapsed by the pulse wave, while the transmission speed of the electromagnetic wave is constant, so the distance from the liquid level to the radar antenna can be calculated, thereby knowing the liquid level of the liquid level.

B.advantage.

The characteristics of not requiring transmission media and not being affected by atmosphere, vapor, or volatile mist in the tank can be used for liquid level measurement of volatile media. Adopting non-contact measurement, it is not affected by the physical characteristics such as density and concentration of the liquid in the tank.

C.shortcoming.

The price is expensive. There are many parameters that need to be set for instruments, and once a problem occurs, it is usually difficult to identify the cause. If the antenna accidentally comes into contact with the medium, it will report an error. If there is crystallization and freezing phenomenon, an error will be reported. Heating and insulation treatment should be carried out, and the antenna should be cleaned.

3. Ultrasonic level gauge

A.working principle.

Ultrasonic level gauge is a digital level instrument controlled by a microprocessor. Pulse ultrasonic waves are measured by sensorsThe transducer emits sound waves, which are reflected off the surface of an object and then received by the same sensor, converting them into electrical signals. And the distance between the sensor and the object being measured is calculated based on the time between the emission and reception of sound waves.

B.advantage.

No mechanical movable parts, high reliability, simple and convenient installation, belonging to non-contact measurement, and not affected by the viscosity, density, etc. of the liquid

C.shortcoming.

The accuracy is relatively low, and testing is prone to blind spots. Pressure vessels and volatile media cannot be measured.

4. Capacitive level gauge

A.working principle.

Measuring the height of the liquid surface by measuring the change in capacitance. It is a metal rod inserted into a liquid container, with the metal rod serving as one pole of the capacitor and the container wall serving as the other pole of the capacitor. The medium between the two electrodes is liquid and the gas above it. Due to the dielectric constant of liquidsε 1 is different from the dielectric constant ε 2 on the liquid surface. For example, if ε 1>ε 2, when the liquid level rises, the total dielectric constant between the two electrodes increases, resulting in an increase in capacitance. On the contrary, when the liquid level drops, the value of ε decreases and the capacitance also decreases. So, the level of liquid can be measured by the change in capacitance between the two electrodes. The sensitivity of a capacitive liquid level gauge mainly depends on the difference between two dielectric constants, and only constant values of ε 1 and ε 2 can ensure accurate liquid level measurement. Due to the conductivity of the measured medium, the metal rod electrode is covered with an insulation layer.

B.advantage.

The sensor has no mechanical movable parts, with a simple and reliable structure; High degree; The detection end consumes less electricity and has fast dynamic response; Easy maintenance and long lifespan. The tested medium must have a conductivity of not less than10-3s/m amorphous conductive liquid.

C.shortcoming.

The instability of the dielectric constant of the tested liquid can cause errors. Capacitive level gauges are generally used for measuring regulating tanks and clean water tanks.(Note: It is unknown whether liquefied gas will affect the measurement.)

5. static pressureDifferential pressure type liquid level gauge

Aworking principle.

Since the static pressure of the liquid column is directly proportional to the liquid level, the liquid level can be measured by measuring the static pressure of the liquid column on the reference surface with a pressure gauge. Calculate the pressure or differential pressure range based on the density of the measured medium and the measurement range of the liquid, and then select a pressure gauge or differential pressure gauge with suitable performance such as range and degree.

B.advantage.

Widely popularized and easy to calibrate.

C.shortcoming.

Due to the significant influence of medium density and temperature, the accuracy is often poor. To eliminate these effects, many other testing instruments are needed, resulting in a high cost for building a complete static pressure measurement system.

6. Magnetostrictive level gauge

A.working principle.

The electronic components at the upper end of the probe generate low-voltage current pulses, which start timing and generate a magnetic field that propagates downward along the magnetostrictive line. The float moves up and down along the measuring rod as the liquid level changes. There is a magnet inside the float, which also generates a magnetic field. When the two magnetic fields meet, the magnetostrictive line twists to form a torsional stress wave pulse. The pulse velocity is known, and the calculated pulse propagation time corresponds to the liquid level change.

B.advantage.

High precision. Suitable for oily liquids.

Cshortcoming.

Installation and maintenance are complex, and the market penetration rate is low.(Note: The pulse principle may also have the disadvantages of radar level gauges)